Police conduct during a traffic stop is limited by Fourth Amendment protections against unreasonable search and seizure. If police observe a traffic violation, they can stop the vehicle and question the driver. The scope of their conduct is restricted to an investigation of the crime or violation that they believe has occurred. Searching a vehicle is an escalation of the scope of the stop (seizure) and also extends the duration of the stop.
Unless the police have a reasonable articulable suspicion of other criminal activity, their conduct during a traffic stop is restricted to investigating only the traffic offense. If police ask for “permission” to search your vehicle, you should be free to say no. If police have a search warrant or if they say that they are going to search with or without your permission, you should not physically interfere with them.
There can be benefits to affirmatively stating that you have not consented to the police search. But each situation will have different facts affecting what will make the most sense. If you have the ability to use your phone, calling an attorney for advice can be your best course of action.